This invention relates generally to devices for controlling a cursor on a display screen, also known as pointing devices. This invention relates more particularly to a system and method for reducing power consumption in an optical pointing device.
The use of a hand operated pointing device for use with a computer and its display has become almost universal. By far the most popular of the various devices is the conventional (mechanical) mouse, used in conjunction with a cooperating mouse pad. Centrally located within the bottom surface of the mouse is a hole through which a portion of the underside of a rubber-surfaced steel ball extends. The mouse pad is typically a closed cell foam rubber pad covered with a suitable fabric. Low friction pads on the bottom surface of the mouse slide easily over the fabric, but the rubber ball does not skid. Rather, the rubber ball rolls over the fabric as the mouse is moved. Interior to the mouse are rollers, or wheels, that contact the ball at its equator and convert its rotation into electrical signals representing orthogonal components of mouse motion. These electrical signals are coupled to a computer, where software responds to the signals to change by a xcex94X and a xcex94Y the displayed position of a pointer (cursor) in accordance with movement of the mouse. The user moves the mouse as necessary to get the displayed pointer to a desired location or position. Once the pointer on the screen points at an object or location of interest, a button on the mouse is activated with the fingers of the hand holding the mouse. The activation serves as an instruction to take some action, the nature of which is defined by software in the computer.
In addition to mechanical types of pointing devices like a conventional mouse, optical pointing devices have also been developed, such as those described in the incorporated patents and patent application. In one form of an optical pointing device, rather than using a moving mechanical element like a ball in a conventional mouse, relative movement between an imaging surface, such as a finger or a desktop, and photo detectors within the optical pointing device, is optically sensed and converted into movement information.
It would be desirable to reduce the power typically consumed by an optical pointing device. Limiting power consumption is particularly important for portable electronic devices, such as portable computers, cellular telephones, personal digital assistants (PDAs), digital cameras, portable game devices, pagers, portable music players (e.g., MP3 players), and other similar devices that might incorporate an optical pointing device.
Some optical motion sensors for optical pointing devices include a low-power mode that is automatically entered if no motion is detected for a period of time. In low power mode, power savings is achieved by turning off a light source of the optical pointing device. The light source is a major contributor to power consumption. The light source is turned back on if the optical motion sensor detects any movement, or the light source is periodically turned back on to facilitate motion detection. In some existing optical motion sensors, an undesirable switch from the low power mode to a full power mode can be caused by noise. If the optical motion sensor is on a border between pixels, the optical motion sensor may report oscillations in motion as it attempts to determine whether it is positioned just over or just under the next pixel step threshold, which causes the optical motion sensor to leave the low power mode. In addition, reasonably slow drift motions, such as those caused by vibrations around an optical mouse, or those caused by placing an optical mouse on a surface with a slight incline, can cause an optical motion sensor to undesirably exit the low power mode.
In the low power mode in some optical motion sensors, images are captured, but at a significantly reduced rate compared to the rate at which images are captured in the full power mode. Some optical motion sensors provide 1500 xe2x80x9cframe periodsxe2x80x9d per second. An image may or may not be captured during a frame period. For example, in full power mode, an image may be captured during each frame period, resulting in 1500 images per second. In low power mode, an image may only be captured every 10 or 12 frame periods, resulting in 125-150 images per second. In full power mode, the light source typically remains on for all frame periods, and is not turned off during a frame period or between frame periods. In low power mode, the light source is typically turned on only during frame periods when images are captured, but remains on for the duration of those frame periods. Turning the light source on for only one frame period out of every 10 frame periods results in a reduction of the power used for illumination of about 90 percent. It would be desirable to provide further power savings in the low power mode, as well as a reduction in power consumption in the full power mode.
Regardless of which mode an optical motion sensor is in, the light source remains on for the entire frame period when an image is captured. However, light is only needed for a small portion of a frame period. A frame period includes three phasesxe2x80x94an integration phase, an analog to digital conversion phase, and an image processing phase. Light is only needed during a portion of the integration phase when an xe2x80x9celectronic shutterxe2x80x9d is open, allowing light to be collected. Power is unnecessarily consumed by leaving the light source on for the entire frame period.
It would be desirable to provide an optical screen pointing device with reduced power consumption.
One form of the present invention provides an apparatus for controlling the position of a screen pointer for an electronic device having a display screen. The apparatus includes a light source for illuminating an imaging surface, thereby generating reflected images. The apparatus includes a motion transducer. A lens receives the reflected images and directs the reflected images onto the motion transducer. The motion transducer includes an electronic shutter for controlling the amount of time that light is collected for image frames. The motion transducer is configured to generate digital representations of the reflected images. The motion transducer is configured to generate movement data based on the digital representations of the reflected images. The movement data is indicative of relative motion between the imaging surface and the motion transducer. A controller coupled to the light source turns the light source on only during the time that light is being collected for an image frame.
Another form of the present invention provides a method of controlling the position of a screen pointer for an electronic device having a display screen. Light is directed from a light source onto an imaging surface, thereby generating reflected images. The reflected images are focusd onto an array of photo detectors. Output values of the photo detectors are digitized, thereby generating digital representations of the reflected images. At least one version of a first one of the digital representations is correlated with at least one version of a second one of the digital representations to generate motion data indicative of relative motion between the imaging surface and the array of photo detectors. The light source is turned off during the digitizing and correlating steps. The position of the screen pointer is adjusted in accordance with the motion data.
Another form of the present invention provides an apparatus for controlling the position of a screen pointer for an electronic device having a display screen. The apparatus includes a light source for illuminating an imaging surface, thereby generating reflected images. The apparatus includes a motion transducer. A lens receives the reflected images and directs the reflected images onto the motion transducer. The motion transducer includes an electronic shutter for controlling the amount of time that light is collected for image frames. The motion transducer is configured to generate digital representations of the reflected images. The motion transducer is configured to generate movement data based on the digital representations of the reflected images. The movement data is indicative of relative motion between the imaging surface and the motion transducer. A controller calculates a time average of the movement data. The controller is configured to determine whether to switch the apparatus from a low power mode to a full power mode based on the calculated time average.
Another form of the present invention provides a method of switching an optical screen pointing device from a low power mode to a full power mode. A first movement is detected with the optical screen pointing device. A first value representing an amount of the first movement is calculated. An accumulated movement value representing an accumulation of previously detected movements is stored. The accumulated movement value is updated by adding the first value. The updated accumulated movement value is compared to a threshold value. It is determined whether to switch to the full power mode based on the comparison of the updated accumulated movement value and the threshold value.